I would just live on. This question although interesting doesn't leave much to consider as you would have no control or decision in how it happened. Hypothetical questions are better when they leave you with some sort of choice or difficult decision. Good examples would be the classic "fuck, marry, kill" or Saw trap decisions. I'm not saying ask questions already asked but saying propose scenarios with some sort of decision or choice that needs to be made (preferably one with many possible options and no easy answer) as that can lead to more interesting discussion.

I'd probably faint or die of a heart attack if that happened. I assume my family would think this random guy saying he's their relative is nuts, but I assume if there's a reason to memorize my Social then there's that reason

I would definitely feel the worse guilt imaginable but in their honor for their sacrifice it would be my obligation to live life to the fullest otherwise their sacrifice would be in vain, and I couldn't live with that. I would also do whatever I could to help take care of their family.